1. Field of the Invention
The present invention relates to a data processing apparatus and a method of expanding dot arrangement patterns, and more particularly to those expansion patterns of dot arrangement patterns which are employed for binarizing image data that has been quantized.
2. Description of the Related Art
With the recent spread of information processing equipment such as personal computers, printing apparatuses for printing images also have been developed and have come into wide use rapidly in various forms of types, contents, etc. Among the various printing apparatuses, especially an ink-jet printing apparatus, which ejects ink from an ejection opening so as to perform printing on a printing medium such as paper, cloth, a plastics sheet or a sheet for OHP, has become a mainstream printing apparatus. The apparatus of this type has the very excellent advantages of being a printing scheme of non-impact type which emits low noise, being capable of a high-density and high-speed printing operation, being easily adapted for color printing, being low in price, and so forth.
In the ink-jet printing apparatus having such advantages, the resolution of an image is increased by making ink droplets smaller, whereby the image quality of the printed image, etc. is still improved. Due to such a higher resolution, however, the quantity of data to be processed in the apparatus becomes enormous. As a result, a print system which includes the ink-jet printing apparatus and a host apparatus such as a computer or the like creates problems that a processing time period in the host apparatus, the time period of data transfer from the host apparatus to the ink-jet printing apparatus, etc. become long. A further problem is that a memory capacity required in the ink-jet printing apparatus needs to be enlarged, and thus an increase in cost is caused.
A method which performs binarization by employing dot arrangement patterns is effective for such problems. With this method, image data are quantized at a comparatively low resolution in, for example, the host apparatus. Then, the quantized multiple-valued image data are transferred to the ink-jet printing apparatus, and the image data received by the printing apparatus are expanded into binary (dot) data by employing the dot arrangement patterns (refer to Japanese Patent Laid-Open No. 09-046522 and Japanese Patent Laid-Open No. 3,610,250). Since the binarization employing the dot arrangement patterns processes and transfers the data of the low resolution in this manner, the data processing and transferring time periods can be prevented from becoming very long, and the memory capacity in the printing apparatus can be made small.
However, the prior-art binarization process employing the dot arrangement patterns may cause problems, especially in the way of expanding the patterns.
FIGS. 1A and 1B are diagrams for explaining the way of expanding dot arrangement patterns in the prior art.
FIG. 1A shows the dot arrangement patterns for binarizing data that has been quantized to be five values, and the dot arrangement patterns correspond to level “1” among the five values (levels “0”-“4”). In the figure, each part painted black indicates (“1”) binary data for forming a dot, and each white part indicates (“0”) binary data which does not form the dot. As just described, the dot arrangement patterns exemplified in the figure are configured in units of (two constituent pixels)×(two constituent pixels). Using these patterns can allow data processing, data transfer, etc. to be executed at a resolution of ½ in both length and width, with respect to binary image data which are finally obtained by expanding the pattern.
The dot arrangement patterns as stated above are expanded for quantized multiple-valued data, as described below. When the multiple-valued data of the level “1”, for example, is inputted, one of the patterns A, B, C and D exemplified in FIG. 1A is selected in correspondence with the pixel position of the multiple-valued data, and dot data is set at a pixel of double resolution in both the length and width (size of 2 constituent pixels×2 constituent pixels) corresponding to the multiple-valued data.
As a method of arranging or expanding patterns for the respective pixel positions for selecting the dot arrangement pattern, there has been known a method (hereinafter, also referred to as “tile expansion”) wherein the patterns are periodically arranged or expanded as shown in FIG. 1B. Alternatively, there has been known a method (hereinafter, also referred to as “pseudo-random expansion”) wherein pseudo-random numbers are generated for A, B, C and D representative of patterns, and the patterns A, B, C and D are arranged or expanded in accordance with the random numbers. In the binarization process, one dot arrangement pattern is selected correspondingly to the pixel position of the multiple-valued data, in accordance with the expansion patterns of the patterns A, B, C and D whose arrangements are determined as stated above. More specifically, in a case where the multiple-valued data are of five values, the patterns A, B, C and D are determined for each of the levels “0”-“4”, one of the patterns A, B, C and D corresponding to the level indicated by the inputted multiple-valued data is selected in the above stated way.
However, in the case where the dot arrangement pattern is selected in accordance with the expansion patterns in the prior art, a deviation sometimes occurs in formed dots, resulting from the method of selecting the dot arrangement pattern in the expansion patterns. By way of example, in the case of employing the periodic expansion patterns as shown in FIG. 1B, a texture sometimes appears in an image actually printed by a printing apparatus. More specifically, when the landing positions of ink deviate due to the errors of the ejection precision of a print head and the precision of the printing apparatus, the deviations appear as the periodic deviation of the dots, and the deviation is visually recognized as the texture in some cases. Further, in the case of employing the expansion patterns based on the pseudo-random numbers, several dots deviate to form bulk dots, and the bulk dots are visually recognized as a granular feeling in some cases.
As stated above, with any type of expansion patterns in the prior art, the plurality of species of dot arrangement patterns for each level, such as the patterns A, B, C and D, are not arranged in appropriately dispersed fashion, so that the deviation occurs in the formed dots and degrades an image quality in a printed image.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.